He has trekked 370 miles of Arabian desert, rowed naked across 2,000 miles of the Atlantic Ocean, survived a traumatic brain injury during a 2010 cycling accident, and was part of Cambridge University’s triumphant team in last year’s Boat Race.
It would be fair to say that Olympic champion James Cracknell enjoys a challenge. But was his latest stunt, which he completed last week, his riskiest yet?
Last Saturday, the 48-year-old father-of-three embarked on what would seem, at first glance, a relatively harmless, if impressive, endeavour: running 100 miles over five days. Only, as he revealed to his 90,000 Twitter followers, he had decided to do so without eating anything for the duration.
Cracknell and his seven team-mates – including bloggers and healthcare professionals – fuelled themselves on water and the occasional black coffee. Two of the group have type 1 diabetes, a condition in which the body does not produce insulin – the hormone needed to metabolise food for fuel – meaning they are at an increased risk of a potentially fatal seizure if they go for too long without food.
Perhaps unsurprisingly, the stunt has been branded ‘dangerous’, ‘irresponsible’ and, in the words of Dr Giles Yeo, a Cambridge University obesity expert, ‘a really, really stupid idea’.
Cracknell, however, has a point to prove. He has claimed the body can fuel itself on its fat stores alone, and that the daily 260g of carbohydrates recommended by UK health guidelines has no scientific basis.
James Cracknell’s 100-mile run over five days has been branded ‘dangerous’, ‘irresponsible’ and, in the words of Dr Giles Yeo, a Cambridge University obesity expert, ‘a really, really stupid idea’
The theory, popular with many low-carb converts, is that once the body runs out of carbohydrates – rapidly converted to sugar and utilised for energy – it burns fat, prompting speedier weight loss.
His second goal is to show that a low-carb diet is an effective therapeutic treatment for diabetes and beneficial for pre-diabetics.
Despite the criticism from some medics, others were supportive. Four healthcare professionals, including an NHS GP and a specialist in child eating disorders, were involved in the challenge, with some participating themselves. And former Labour Party deputy leader Tom Watson, who claims he lost 8st as a result of cutting carbs, wrote: ‘I wish I was with you!’
So, is it really as stupid an idea as it might seem? According to daily YouTube videos posted by Cracknell’s fellow runner Steve Bennett, founder of supplement company Primal Living, the challenge was a ‘science-breaking’ success, with participants finishing on ‘high energy’ and with no health complications.
But according to Renee McGregor, a specialist dietician who works with Team GB athletes, they had a lucky escape.
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Extreme dehydration, certain drugs and high-protein diets can increase the risk of them developing. The pain they cause may lead to hospitalisation.
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Cracknell’s health claims about the benefits of fasted exercise – especially for type 1 diabetics – is ‘scarily incorrect’, says McGregor.
Unlike type 2 diabetes, which studies have shown can, in some cases, be put into remission via a weight-loss diet, type 1 diabetes is caused by the immune system and cannot be treated with lifestyle changes alone. Type 1 diabetics need regular injections of the vital hormone insulin, which helps the body absorb sugar, used for energy, from food. And for them, eating nothing at all can be fatal, especially while exercising, says Dr Yeo.
‘First there’s a chance of hypoglycaemia, when the blood sugar levels drop drastically, risking brain damage, coma, or even sudden death,’ he adds. ‘Even if you’ve eating lots previously and you’re not injecting insulin – keeping blood sugar high – exercising for long periods while starving yourself makes hypoglycaemia more likely. The dangerous drops in blood sugar can happen at a moment’s notice in type 1 diabetics.’
Then there’s the risk that the blood could become dangerously acidic, a state known as ketoacidosis, which Dr Yeo says could also become fatal ‘within hours’. ‘Acidic compounds called ketones build up when the body burns its own fat,’ he explains. ‘But this can quickly become uncontrolled in people with type 1 diabetes. Even a slight increase in the acidity of the blood could put you in a coma within hours, if left untreated.’
According to NHS guidance, a blood ketone level above 0.6mmol is a cause for concern. On day four of the challenge, participant Jon Furniss, an engineer who has type 1 diabetes, wrote on his Twitter feed that his ketones measured 5.8mmol – more than eight times the NHS’s safe limit.
Furniss added: ‘Ketones alone do not signal ketoacidosis, that happens after VERY high blood glucose. My BG [blood glucose, or blood sugar level] has been normal throughout.’
Yet a wealth of medical studies contradict this.
Low-carb diet club diabetes.co.uk says: ‘In most cases, ketoacidosis in people with diabetes will be accompanied by high sugar levels. However, ketoacidosis can also occur at low or normal blood glucose levels. This may occur if someone who is insulin dependent neither eats nor takes sufficient insulin for a prolonged period of time.’
And the risks of a fasting marathon don’t apply only to diabetics – it could harm healthy people, too.
‘Research shows that even two or three 60-minute sessions of exercise without eating before can dramatically suppress the immune system because of an increase in stress hormones, ‘ says McGregor.
Cracknell claims the body can fuel itself on its fat stores alone, and that the daily 260g of carbohydrates recommended by UK health guidelines has no scientific basis
‘Studies on marathon runners show that competitors are highly susceptible to bacterial and viral infections for a week afterwards, which isn’t ideal at this current time. Even after five days of fasting while exercising there’s likely to be a dramatic drop in sex hormones, affecting everything from cognitive function to bone health to fertility.’
Professor Mike Gleeson, an expert in exercise physiology at Loughborough University, has serious concerns. ‘It doesn’t take long to become deficient in minerals and vitamins we don’t store well, including Vitamins C and B – essential for healthy blood cells and providing organs and muscle with enough energy to function. You’ll quickly become deficient in protein, so you’re likely to lose quite a bit of muscle.’
And rather than improving athletic performance, as suggested by some of Cracknell’s supporters, running on empty will hinder it.
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‘It’s hard for the body to use fat for energy, and when it can’t be broken down quickly enough, the body will begin to break down muscle, increasing the risk of strains,’ says McGregor. ‘Most people would eventually just hit a wall.’
And this, say the experts, is why carbohydrates are crucial. ‘When we consume carbs, they’re broken down into glucose and absorbed into cells where it’s used for energy. But this process also triggers the release of chemicals that help break down fat, which can then also be used as fuel,’ says Dr Yeo.
Tellingly, on day two, more than 20 miles into the challenge, Steve Bennett reported feeling ‘thoroughly miserable’ and ‘void of energy’. He said: ‘I feel lousy and miserable. My feet ache, my knees ache, my toes ache – and we still have three days to go.’
According to McGregor, carbohydrates are the body’s ‘preferred currency for energy’. ‘The body is very efficient at converting glucose to energy,’ she says. ‘And muscles will only get bigger and stronger if there are sufficient carb stores in the system.’
So if you wish to partake in an extreme physical challenge, such as a 100-mile run, what should you eat? At least two pasta bowls’ worth of carbohydrates daily, and roughly three chicken breasts’ worth of protein, say the experts.
Renee McGregor adds: ‘Beforehand, eat something slow-releasing, such as porridge or toast with a banana and peanut butter, and then stop every couple of hours to fuel again on something similar. Trying to eat less isn’t just pointless, it’s harmful.’
Did Cracknell prove what he set out to prove? On Thursday, Bennett reported that all the participants had completed the challenge, then had a ‘nice meal’. ‘All our markers were stable throughout, and all finished with high energy and spirits,’ he added.
It’s been hinted a documentary is planned that will give full details. Dr Yeo is sceptical anything could be gained from such an experiment, saying: ‘It doesn’t prove anything. It’s an entirely pointless exercise.’
And McGregor has a stark warning for anyone considering giving it a go: ‘I wouldn’t recommend anyone tries this, especially those with type 1 diabetes. It’s too dangerous.’
In a statement, James Cracknell said that all eight participants completed the challenge, with ‘no issues whatsoever’ – and insisted it was ‘thoroughly researched’ and carried out after consultation with experts. He said: ‘The project was set up to explore the potential of fat-burning metabolism in diabetes and sport by taking it to extremes.
‘Renee McGregor is quite right, this should not be repeated by people with type 1 diabetes – it was never the point of this project to be a recommendation. No type 1 diabetics should undertake changes to their management without medical consultation. and they should never stop taking insulin as this can be fatal.’
He added: ‘The project was not reckless or stupid but a serious scientific endeavour.’